Flexibly scalable charge balanced vertical semiconductor power devices with a super-junction structure

ABSTRACT

This invention discloses a semiconductor power device disposed in a semiconductor substrate and the semiconductor substrate has a plurality of deep trenches. The deep trenches are filled with an epitaxial layer thus forming a top epitaxial layer covering areas above a top surface of the deep trenches covering over the semiconductor substrate. The semiconductor power device further includes a plurality of transistor cells disposed in the top epitaxial layer whereby a device performance of the semiconductor power device is dependent on a depth of the deep trenches and not dependent on a thickness of the top epitaxial layer. Each of the plurality of transistor cells includes a trench DMOS transistor cell having a trench gate opened through the top epitaxial layer and filled with a gate dielectric material.

This is a Divisional Application of a previously filed co-pendingApplication with a Ser. No. 12/807,116 filed on Aug. 26, 2010 byidentical common inventors of this Application. Application with Ser.No. 12/807,116 is a Divisional Application of another application Ser.No. 12/229,250 filed on Aug. 20, 2008 by identical common inventors ofthis Application and now issued into U.S. Pat. No. 7,790,549. Thedisclosures made in application Ser. Nos. 12/807,116 and 12/229,250 arehereby incorporated by reference in this patent application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the vertical semiconductor powerdevices. More particularly, this invention relates to configurations andmethods implemented with a single thin epitaxial layer with improvedmanufacturability for manufacturing flexibly scalable charge balancedvertical semiconductor power devices with a super-junction structurewith simple manufacturing processes independent of the targetedbreakdown voltage.

2. Description of the Prior Art

Conventional manufacturing technologies and device configuration tofurther increase the breakdown voltage with reduced series resistanceare still confronted with manufacturability difficulties. The practicalapplications and usefulness of the high voltage semiconductor powerdevices are limited due to the facts that the conventional high powerdevices generally have structural features that require numeroustime-consuming, complex, and expensive manufacturing processes. As willbe further discussed below, some of the processes for manufacturing thehigh voltage power devices are complicated thus having low throughputand low yields. Furthermore, instead of using a raw semiconductor wafer,the semiconductor power devices are generally fabricated withpreprocessed wafer formed with an epitaxial layer thereon. Theproduction costs of the semiconductor power devices are thereforeincreased. Also, the functionality and performance characteristics areoften dictated by the process parameters applied in forming thisepitaxial layer. For these reasons, the application of such preprocessedwafers further limits the manufacturability and the productionflexibility of the power devices that are now dependent on the originalpreprocessed wafer employed to manufacture the semiconductor powerdevices.

In comparison to conventional technologies, the super-junctiontechnologies have advantages to achieve higher breakdown voltage (BV)without unduly increasing the Rdson resistance. For standard powertransistor cells, breakdown voltage is supported largely on thelow-doped drift layer. Therefore, the drift layer is made with greaterthickness and with relatively low doping concentration to achieve highervoltage ratings. However this also has the effect of greatly increasingthe Rdson resistance. In the conventional power devices, the resistanceRdson has approximately a functional relationship represented by:Rdson∝BV^(2.5)In contrast, a device having a super-junction configuration isimplemented with a charge balanced drift region. The resistance Rdsonhas a more favorable functional relationship with the breakdown voltage.The functional relationship can be represented as:Rdson∝BVFor high voltage applications, it is therefore desirable to improve thedevice performance by designing and manufacturing the semiconductorpower devices with super-junction configurations for reducing theresistance Rdson while achieving high breakdown voltage. Regionsadjacent to the channel within the drift region are formed with anopposite conductivity type. The drift region may be relatively highlydoped, so long as the regions adjacent to the channel are similarlydoped but of an opposite conductivity type. During the off state, thecharges of the two regions balance out such that the drift, regionbecomes depleted, and can support a high voltage. This is referred to asthe super-junction effect. During the on state, the drift region has alower resistance Rdson because of a higher doping concentration.

However, conventional super-junction technologies still have technicallimitations and difficulties when implemented to manufacture the powerdevices. Specifically, multiple epitaxial layers and/or buried layersare required in some of the conventional structures. Multiple etch backand chemical mechanical polishing (CMP) processes are necessary in manyof the device structures according to the previous manufacturingprocesses. Furthermore, the manufacturing processes often requireequipment not compatible with standard foundry processes. For example,many standard high-volume semiconductor foundries have oxide CMP(chemical mechanical polishing) but do not have silicon CMP, which isrequired for some superjunction approaches. Additionally, these deviceshave structural features and manufacturing processes not conducive toscalability for low to high voltage applications. In other words, someapproaches would become too costly and/or too lengthy to be applied tohigher voltage ratings. As will be further reviewed and discussionsbelow, these conventional devices with different structural features andmanufactured by various processing methods, each has limitations anddifficulties that hinder practical applications of these devices as nowdemanded in the marketplace.

There are three basic, types of semiconductor power device structuresfor high voltage applications. The first type includes those deviceformed with standard structures as depicted in FIG. 1A for a standardVDMOS that do not incorporate the functional feature of charge balance.For this reason, there is no breakdown voltage enhancement beyond theone-dimensional theoretical figure of merit, i.e., the Johnson limit,according to the I-V performance measurements and further confirmed bysimulation analyses of this type of devices. The devices with thisstructure generally have relatively high on-resistance due to the lowdrain drift region doping concentration in order to satisfy the highbreakdown voltage requirement. In order to reduce the on resistanceRdson, this type of devices generally requires large die size. Despitethe advantages that the devices can be manufactured with simpleprocesses and low manufacturing cost, these devices are however notfeasible for high current low resistance applications in the standardpackages due the above discussed drawbacks: the die cost becomesprohibitive (because there are too few dies per wafer) and it becomesimpossible to fit the larger die in the standard accepted packages.

The second type of devices includes structures provided withtwo-dimensional charge balance to achieve a breakdown voltage higherthan the Johnson limit for a given resistance, or a lower specificresistance (Rdson*Area product) than the Johnson limit for a givenbreakdown voltage. This type of device structure is generally referredto as devices implemented with the super junction technology. In thesuper junction structure, a charge-balance along a direction parallel tothe current flow in the drift drain region of a vertical device, basedon PN junctions such as CoolMOS™ structures by Infineon, and field platetechniques implemented in oxide bypassed devices to enable a device toachieve a higher breakdown voltage. The third type of structure involvesa three-dimensional charge-balance where the coupling is both in thelateral as well as the vertical directions. Since the purpose of thisinvention is to improve the structural, configurations and manufacturingprocesses of devices implemented with super junction technologies toachieve two-dimensional charge balance, the limitations and difficultiesof devices with super junction will be reviewed and discussed below.

FIG. 1B is a cross sectional view of a device with super junction toreduce the specific resistance (Rsp, resistance times active area) ofthe device by increasing the drain dopant concentration in the driftregion while maintaining the specified breakdown voltage. The chargebalance is achieved by providing P-type vertical columns formed in thedrain to result in lateral and complete depletion of the drain at highvoltage to thus pinch off and shield the channel from the high voltagedrain at the N+ substrate. Such technologies have been disclosed inEurope Patent 0053854 (1982), U.S. Pat. No. 4,754,310, specifically inFIG. 13 of that patent and U.S. Pat. No. 5,216,275. In these previousdisclosures, the vertical super junctions are formed as vertical columnsof N′ and P type dopant. In vertical DMOS devices, the vertical chargebalance is achieved by a structure with sidewall doping to form one ofthe doped columns as were illustrated in drawings. In addition to dopedcolumns, doped floating islands have been implemented to increase thebreakdown voltage or to reduce the resistance as disclosed by U.S. Pat.Nos. 4,134,123 and 6,037,632. Such device structure of super junctionstill relies on the depletion of the P-regions to shield thegate/channel from the drain. The floating island structure is limited bythe technical difficulties due to charge storage and switching issues.

For super junction types of devices, the manufacturing methods aregenerally very complex, expensive and require long processing time dueto the facts that the methods require multiple steps and several ofthese steps are slow and have a low throughput. Specifically, the stepsmay involve multiple epitaxial layers and buried layers. Some of thestructures require deep trenches through the entire drift region andrequire etch back or chemical mechanical polishing in most theseprocesses. For these reasons, the conventional structures andmanufacture methods are limited by slow and expensive manufacturingprocesses and are not economical for broad applications.

Therefore, a need still exists in the art of power semiconductor devicedesign and manufacture to provide new device configurations andmanufacturing method in forming the power devices such that the abovediscussed problems and limitations can be resolved.

SUMMARY OF THE PRESENT INVENTION

It is therefore an aspect of the present invention to provide a new andimproved device structure and manufacturing method to form the dopedcolumns in the drift regions for charge balance with simple andconvenient processing steps achieved through doping trench sidewalls ofdeep trenches that do not extend through the entire vertical driftregion. There are no etch-backs or CMP (chemical mechanical polishing)required thus reducing the processing steps and can be implemented withjust forming a single thin epitaxial layer, grown in a vertical trenchand on the top surface on the areas surrounding the trench to achievethe super-junction structure. The deep trench is located in the driftregion, and provides the super-junction effect through charge balancewith the drift region. The structure and configuration of the superjunction structure as that disclosed in this invention may beimplemented independent of the targeted range of the breakdown voltages.The manufacturing processes are simplified and can be convenientlymanufactured with standard processing using standard processing modulesand equipment. The manufacturing processes are further simplifiedbecause the transistor portion of the structure, e.g., the trench gateDMOS, is self-aligned. Therefore, the above discussed technicaldifficulties and limitations can be resolved.

Specifically, it is an aspect of the present invention to provide a newand improved device structure and manufacturing method to form theP-epitaxial layer in a vertical trench with the P-epitaxial layerincluding a thin top epitaxial layer covering over the top surface ofthe surrounding areas above the vertical trenches. The P-epitaxial layerfilling the trench, and the thin top epitaxial layer are actually thesame single epitaxial layer, grown simultaneously. The MOSFET transistorcells are formed in this top thin epitaxial layer. Trench gates areopened through the top thin epitaxial layer with trench sidewalls andtrench bottom dopant implant zones to eliminate the sensitivity of thechannel performance that may be affected by the depth of the trenchgates and the dopant concentration of the P-epitaxial layer. The trenchgates allow the formation of vertical channels connected the sourceregion formed on top of the drift region in the semiconductor substrate.The performance of the transistor cells can be well controlled andadjusted by simplified and conveniently processing steps. Thesuper-junction configurations disclosed in this invention is furtherscalable for broad ranges of applications.

It is another aspect of the present invention to provide a new andimproved device structure and manufacturing method to form the powertransistor cells on a thin top layer formed as a P-epitaxial layercovering over vertical trenches on the top surface surrounding areasabove the vertical trenches. Before the deep trenches are filled withthe P-epitaxial layer, an ion implant is carried out through thesidewalls of the deep trenches to adjust the dopant concentration of theregions surrounding the deep trenches. The N-dopant implant thusprovides N-column charge control to further adjust and tune theperformance of the semiconductor power devices for different type ofapplications.

It is another aspect of the present invention to provide new andimproved device structure and manufacturing method to form the powertransistor cells with shallow trench gates on thin top P-epitaxial layercovering over vertical trenches on the top surface surrounding areasabove the vertical trenches. Flexible device channel performance can beadjusted and implemented with a trench bottom dopant implant andsidewall dopant implants. The sidewall dopant implants and the trenchbottom implant are applied to compensate the P-epitaxial and to assureappropriate accumulation and the channel regions.

It is another aspect of the present invention to provide new andimproved device structure and manufacturing method to form the powertransistor cells with deeper trench gates in a thin top layer formed asa P-epitaxial layer covering over vertical trenches on the top surfacesurrounding areas above the vertical trenches. The deep trench gatespenetrate through the top thin epitaxial layer and extend into the Nsubstrate regions thus a trench bottom dopant implant may no longernecessary.

Briefly in a preferred embodiment this invention discloses asemiconductor power device disposed in a semiconductor substrate and thesemiconductor substrate has a plurality of deep trenches. The deeptrenches are filled with an epitaxial layer and a top epitaxial layercovering areas above a top surface of the deep trenches covering overthe semiconductor substrate. The semiconductor power device furtherincludes a plurality of transistor cells disposed in the top epitaxiallayer whereby a device performance of the semiconductor power device isdependent on a depth of the deep trenches and not dependent on athickness of the top epitaxial layer. Each of the plurality oftransistor cells includes a trench DMOS transistor cell having a trenchgate opened through the top epitaxial layer and filled with a gatedielectric material. In an exemplary embodiment, each of the pluralityof transistor cells includes a trench DMOS transistor cell having atrench gate opened through the top epitaxial layer and penetrating intoa top portion of the semiconductor substrate and the trench gate isfilled with a gate dielectric material. In another exemplary embodiment,each of the plurality of transistor cells includes a trench DMOStransistor cell having a trench gate opened through the top epitaxiallayer having a gate trench depth less than or equal to a thickness ofthe top epitaxial layer and the trench gate is filled with a gatedielectric material. In an exemplary embodiment, each of the DMOStransistor cells further having gate sidewall dopant regions surroundingsidewalls of the trench gate and a gate-bottom dopant region below thetrench gate. In an exemplary embodiment, each of the plurality oftransistor cells includes a vertical transistor cell disposed in the topepitaxial layer. The portions of the semiconductor substrate adjacent tothe deep trenches act as the drift layer to the vertical transistors andachieve the super-junction effect through charge balance with theportions of the epitaxial layer in the deep trenches. The semiconductorpower device further includes a drain contact dopant region surroundinga bottom portion of the deep trenches near a bottom surface of thesemiconductor substrate for connecting to a drain electrode. In anotherexemplary embodiment, the semiconductor power device further includes abottom metal layer constituting a drain electrode contact the draincontact dopant region.

This invention further discloses a method for forming a semiconductorpower device on a semiconductor substrate. The method includes a step ofopening a plurality of deep trenches and filling the deep trench with anepitaxial layer overflowing and covering a top surface of thesemiconductor substrate with a top epitaxial layer. The method furtherincludes another step of forming a plurality of transistor cells in thetop epitaxial layer for adjusting a device performance of thesemiconductor power device to depend on a depth of the deep trenches andnot dependent on a thickness of the top epitaxial layer. In an exemplaryembodiment, the method further includes a step of forming dopantgradients in regions of the semiconductor substrate between the deeptrenches by implanting dopant ions through sidewalls of the deeptrenches and adjusting the device performance of the semiconductor powerdevice by adjusting dopant concentrations of the dopant gradients. Inanother exemplary embodiment, the method does not include the step ofimplanting dopant ions through sidewalls of the deep trenches, but formsdoping columns by selects a substrate with the appropriate initialdoping concentration. In another exemplary embodiment, the methodfurther includes a step of controlling a thickness of the top epitaxiallayer by adjusting a width of the deep trenches.

These and other objects and advantages of the present invention will nodoubt become obvious to those of ordinary skill in the art after havingread the following detailed description of the preferred embodiment,which is illustrated in the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1B are cross sectional views for showing conventionalvertical power device configurations manufactured by conventionalmethods.

FIGS. 2 to 8 are cross sectional views of high voltage power deviceswith super junction structure as different embodiments of thisinvention.

FIGS. 9A to 9M are a cross sectional views to illustrate processingsteps of this invention to manufacture high voltage power device of FIG.2 with super junction structures.

FIGS. 10A to 10D are cross sectional views to illustrate processingsteps of this invention to manufacture super-junction power device ofwith shallower trenches.

FIG. 11 is a cross sectional view to illustrate a zero tilt implantprocess to form the drain contact regions below the deep trenches filledwith an epitaxial layer of this invention.

FIGS. 12A to 12M are a series of cross sectional views to illustrateprocessing steps of this invention to manufacture another exemplaryembodiment of a charge-balanced power device with super junctionstructure of this invention.

FIGS. 13A to 13M are a series of cross sectional views to illustrateprocessing steps of this invention to manufacture another exemplaryembodiment of a charge-balanced power device with super junctionstructure of this invention.

DETAILED DESCRIPTION OF THE METHOD

Referring to FIG. 2 for a cross sectional view of a MOSFET device 100that illustrates the new concepts including the new structural andmanufacturing features of this invention. The details of the MOSFETdevice 100 will be further described and explained in FIG. 3. The MOSFETdevice 100 is supported on an N type substrate 105 that includes a N+doped bottom region 120 functioning as drain contact region dopedthrough deep trenches 130 (after back grinding, as shown in FIG. 3below) that is filled with a P-epitaxial layer therein. The MOSFETtransistor cells are supported on the single thin P-epitaxial layerfilling in epitaxial column trenches 130 and covering over the topsurface surrounding the P-epitaxial columns that has the P-epitaxialfilling in the column trenches. The thin P-epitaxial region at the topis formed with the body regions 150 surrounding the trench gate 145filled with gate polysilicon therein. The P-body regions 150 furtherencompass the source regions 155 surrounding the trench gates 145. Notethat the P-epitaxial layer 130 is of an opposite conductivity type asthe N+ substrate region 105. The trench gates 145 is padded with a gateoxide layer 140 and covered with an insulation layer 160 with contactopenings to allow a source contact metal to contact the source-bodyregions between the trench gates 145. The active areas are formed on theflat portions of the P-epitaxial layer, located away from the seamsdirectly over the deep trenches 130. The delicate trench gates areformed in the top portions of the epitaxial layer Between the deeptrenches 130, where the surface is flat and smooth. For this reason, aCMP of the P-epitaxial layer is not required for this device.

The device as shown in FIG. 2 provides a single thin epitaxial layer toform the trench gates with gate polysilicon filled in the trenchesopened therethrough. The new configuration achieves a super-junctionstructure independent of the requirement of a particular breakdownvoltage. The new configuration achieves super-junction performance,i.e., performance below the “Johnson Limit”, with breakdown voltageindependent of the thickness of the epitaxial layer grown on thestarting substrate. It is the depth of the trench into the semiconductorsubstrate (as well as the doping concentration of the substrate and ofany implants and diffusions performed inside the trenches), which setsthe breakdown voltage. The thickness of the epitaxial silicon growth isonly a function of the width of the trenches, which are etched in thesilicon substrate. Conventional devices do not have this flexibility andmust grow epitaxial layers, which have a thickness, proportional to thedesired breakdown voltage.

The structure shown is flexibly scalable and the device can bemanufactured by applying simple manufacturing technologies. For example,a device capable of achieving a low specific resistance below theJohnson Limit, over a wide range of breakdown voltage (200V to 900V forexample) can be realized by using a single epitaxial silicon layergrowth of a few microns, and a single trench etch with a depthproportional to the desired breakdown voltage (about 10-15 micronfor >200V, about 40-50 micron for >600V and about 70-90 micron for>900V).

Furthermore, the transistor portion of the device supported on the topportion of the epitaxial layer 130 is structured as trench-gate DMOSdevice wherein the device configuration is self-aligned and can beconveniently and easily manufactured.

Referring to FIG. 3 for a cross sectional view of a MOSFET device 100with the new concepts and basic structures illustrated in FIG. 2 andmanufactured according the processes described in FIGS. 9A to 9M below.The MOSFET device 100 is supported on an N type substrate includes a N+doped bottom region 120 functioning as drain contact region immediatelyabove and in contact with a bottom drain electrode 110. The draincontact regions 120 are doped through deep trenches 130. Each of thesedeep trenches is filled with a P-epitaxial layer filling the trenchesand covering the surrounding top surfaces over the trenches 130. TheMOSFET transistor cells are supported on the single thin P-epitaxiallayer that fills in epitaxial column trenches 130 and covering over thetop surface surrounding the P-epitaxial columns. The thin P-epitaxiallayer over the top is formed with P-body regions 150 surrounding thetrench gates 145 with gate polysilicon filling in the trenches openedthrough the top epitaxial layer 130. The P-body regions furtherencompass the source regions 155 surrounding the trench gates 145. Thetrench gates 145 are padded with a gate oxide layer 140 and covered withan insulation layer 160 with contact openings to allow a source contactmetal 170 over a metal barrier layer 165 to contact the source-bodyregions between the trench gates 145. The N substrate regions 125surrounding the P-epitaxial columns 130 are implanted with N-dopant tocreate a lateral doping concentration gradient for achieving a N-columncharge control. The Super-Junction effect, or charge balance, isachieved by ensuring that the electrical charges of the P-epitaxiallayer filled in the trenches is laterally balanced, i.e., balanced alongthe distance that is perpendicular to the drain current flow in thedrift region of the vertical MOSFET structure, so that they deplete whenthe MOSFET is in the off state. In other words, the electrical chargesof the P-epitaxial layer filled in the trenches are substantially equalto the electrical charges of the N-drift region adjacent to theN-substrate within the manufacturing tolerances. The electrical chargesin the N-drift region can be controlled and adjusted by controllingeither the doping of the N-substrate, or the doping of the N-substrateplus any additional N-dopant ions, which may be implanted in thesidewalls of the deep trenches. The N-drift region is the portion of thesubstrate 125 that is located above the N+ doped bottom region 120 andbelow the transistors cells. For ideal operation, the P=N=1E12 atoms percubic centimeter is the target charge. The more flexible the control ofthe electrical charges in the manufacturing processing by controllingthe implant dosages, implant annealing, substrate doping concentration,epitaxial dopant concentration, trench depth, width and shape, and theparameters of other processing steps, the more the structure of thedevice can be optimized and fine tuned to achieve a lower specificresistance for a given breakdown voltage.

The MOSFET transistor cells further include N type dopant implantregions 135-S along the gate sidewalls and N type dopant implant regions135-B below the gate trench bottom. The sidewall and bottom dopantimplant regions surrounding the gates 145 are applied to eliminated thesensitivity of the channel of the MOSFET device relative to the trenchdepth and the P-epitaxial dopant concentrations. This embodiment withthe new structure is based on the consideration of forming ahigh-performance MOSFET structure inside the P-epitaxial layer grown onthe N-type substrate. The epitaxial layer is grown with minimal or noetch-back of the P-epitaxial layer at all. For a MOSFET to function, itmust have a source of the same conductivity as the drain, and a body,which has an opposite conductivity, as well as an accumulation region,which connects the channel to the drain. When a trench-gate verticalMOSFET structure is realized, the source is at the top with the channelformed in a body region below the source and along the sidewalls of thegate trenches. An accumulation region must be formed, between the bodyregion and the drain. For a high-voltage structure with the newconfiguration as disclosed in this invention, it would be difficult toform a high-performance vertical trench-gate MOSFET when the P-epitaxialgrown on the top horizontal surfaces of the N-substrate is very thick.With a thick P-epitaxial layer, the gate trenches would have to be deepin order to reach through to the N-drift drain region. A deep trench,combined with a thick P-body region, will result in a low-performancevertical DMOS structure because of the resulting long channel and highchannel resistance. Therefore, in the embodiments of this new inventionwhich deal with P-epitaxial layers which may have a greater thicknessbetween one, to three μm relative to the typical depth of gate trenchesgenerally in a range between 0.8 to 1.5 μm, additional dopant implantsin the gate trench sidewalls and bottom are carried out. The additionaldopant implants are to compensate the P-epitaxial region in theaccumulation and drain regions in proximity to the gate trenches, inorder to realize high performance vertical trench-DMOS devices.Therefore, the addition of the tilted and non-tilted implants in thegate trench prior to the fabrication of the MOSFET device is the gatetrenches enables high-performance trench-gate MOSFET devices independentof the P-epitaxial layer thickness and dopant concentrations in theseregions.

It should be noted that the embodiment of FIG. 3 shows a gate trenchwhich reaches through the P-epitaxial layer, and therefore, the N-typeimplants may be selected to optimize the performance of the MOSFET,without the need to compensate completely the P-doped region, i.e., theP-epitaxial layer, on the gate trench sidewalls. Implant species can bepreferably phosphorus as well as Arsenic or Antimony. Energy can be inthe 50 KeV to 200 KeV range. Tilt angle should be zero for the bottomimplant, and +/−5 to 15 degrees for the sidewall implants. Dose can bein the 1E11 to 1E13 range.

FIG. 4 is a cross sectional view to show an alternate embodiment of aMOSFET device similar to that shown in FIG. 3 except that theN-substrate regions 125′ are not implanted with N dopant to achieve thecharge control function through the manufacturing processes. Thisembodiment does not require the additional N-dopant regions forincorporation in the sidewalls of the deep trenches, because it isassumed that the doping concentration of the starting N-substrate isadequate to ensure charge balance with the grown P type epitaxial layerin the deep trenches. The doping concentration of the startingN-substrate is adequate when the actual value of the dopingconcentration can achieve the necessary charge balance, i.e., achievingthe goal of having approximately absolute value of the N charge=Pcharge=1E12 atoms/cm³. A dopant implant to carry out the charge controlis not necessary when the substrate concentration can achieve the chargebalance goals within the desired tolerance limits (for example, when theoccurrences of N-substrate having adequate dopant concentration hasbetter than +/−10% repeatability in the manufacturing processes).

FIG. 5 is a cross sectional view to show an alternate embodiment of aMOSFET device similar to that shown in FIG. 3, except that the MOSFETdevice does not include a sidewall and trench bottom dopant implantregions 135-B and 135-S shown in FIG. 3. When the trench gates 145 havea greater depth and extend below the epitaxial layer 130 into thesubstrate region 125, and the epitaxial length isn't too long, therequirement for applying the trench sidewall and trench bottom dopantimplant regions to eliminate the channel sensitivity to the depth of thetrench gates are no longer necessary.

FIG. 6 is a cross sectional view to show an alternate embodiment of aMOSFET device similar to that shown in FIG. 3 except that the MOSFETdevice has shallower trench gates with a depth shallower than theepitaxial layer. The MOSFET device includes a gate trench sidewall andgate trench bottom dopant implant regions 135-B and 135-S to compensatethe P-epitaxial layer 130 and to ensure that there are appropriateaccumulation and channel regions. This embodiment is based on aconfiguration that the MOSFET device has a relatively thick P-epitaxiallayers, or shallow gate trenches, or a combination of both. The gatetrenches do not reach to the N drain region. In order to ensure properand efficient transistor operations, the lower portion of the gatetrenches must be doped N to ensure that there will be an accumulationregion to connect the drain to the active channel formed in the bodyregion along the sidewalls of the gate trenches.

Conventional wafers have a heavily doped substrate, with lightly dopedlayer on top. However, the devices in FIGS. 1-6 were made from a plainwafer that did not initially have an epi-layer. This can save aconsiderable amount of the wafer costs, but requires extra steps ofdoping the bottom through the deep trench and back grinding the wafer.Alternatively, the device in FIGS. 7-8 uses a conventional wafer with aheavily doped N+ bottom substrate 121, and a less heavily doped N-typetop substrate layer 126 grown over the N+ bottom substrate 121. In aconventional wafer, this N-type top substrate layer 126 is known as anepitaxial layer, however to avoid confusion, it is referred to in thisapplication as a top substrate layer. FIG. 7 is a cross sectional viewto show a MOSFET device similar to that shown in FIG. 3 except that thedeep trenches 130 filled with P-epitaxial layer is now located in the Nsubstrate layer 126 and extended to touch the highly doped. N+ bottomsubstrate region 121. A separate drain contact region 120 of FIG. 3formed by a separate dopant implant process is no longer required.Instead, a highly doped bottom substrate region 121, (N+ for N-channeldevice) with an N-type top substrate layer 126 grown on top of thisbottom substrate 121 (which is the standard semiconductor waferconfiguration used for most vertical Power devices), is used for thisembodiment. The top substrate region can be thin compared to theepitaxial layer of conventional wafers, thus saving cost. A backsidegrinding might not be required for this embodiment. A metal drainelectrode 110 is to be formed beneath the highly doped substrate region121.

The drain contact dopant implant process (at the bottom of the deeptrenches) is eliminated, which reduces the number of processing stepscompared to earlier embodiments.

FIG. 8 is a cross sectional view to show an alternate embodiment of aMOSFET device similar to that shown in FIG. 7 except that the deeptrenches 130 filled with P-epitaxial layer is now at a depth that isshallower than the highly doped N+ bottom substrate 121 which connectsto metal drain electrode 110.

Referring to FIGS. 9A to 9M for a serial of side cross sectional viewsto illustrate the fabrication steps of a charge balanced semiconductorpower device as that shown in FIG. 2. FIG. 9A shows a starting siliconsubstrate includes an N substrate 205 having a resistivity approximately10 ohm/cm. The N substrate 205 initially has no epitaxial layer. A hardmask oxide layer 212 is deposited or thermally grown with a thickness of0.1 to 1.5 micrometer. Then a trench mask (not shown) with a criticaldimension (CD) in a 1 to 5 microns range, is applied to carry out anoxide etch to open a plurality of trench etching windows followed byremoval of the photoresist. A silicon etch, is carried out to open deeptrenches 214 with a depth of 40 to 50 microns for devices operated at avoltage of about 650 volts. Depending on the type etcher and etchchemistries, a photoresist only mask may also be used to pattern andopen the trench as well instead of using the hard mask oxide layer 212as shown. The trench opening may be in the 1 micron to 5 microns rangepreferably 3 microns for most applications (the trench opening beingdefined by the trench mask mentioned earlier). Then a wafer cleanprocess is performed. In FIG. 9B, a conformal oxide layer 215 is formedby either an oxide deposition or thermal growth process. Then anoptional RIE anisotropic etch is carried out to clear the oxide from thebottom of the trench bottom surface if the oxide layer is thicker on thebottom surface. The thickness of the oxide layer 215 is between 0.015 to0.1 micron, when the process does not include the optional RIE step andthe layer thickness of the oxide layer 215 is between 0.1 to 0.4micrometers when the processes include the optional RIE step. A draincontact implant is performed by implanting N+ ions along a zero tiltangle relative to the sidewalls of the trenches, i.e., a verticalimplant, having an implant dosage greater than 1E15 to form the draincontact regions 220 immediately below the deep trenches 214. The draincontact region 220 may be implanted with N ions such as phosphorus orarsenic ions. The oxide layer 215 along the sidewalls protects thesidewalls from the high dosage of the drain contact implant.

In FIG. 9C, a trench sidewall implant is carried out With N-type ionssuch as phosphorous ions to set the doping concentration in the Nregions. An implant with tilted angle and rotated operations areperformed with a dosage of 5E11 to 2E13 and a tilt angle of five tofifteen degrees are carried out to form the N-regions 225 between thetrenches depending on the trench depth. In FIG. 9D, a high temperatureanneal operation at 1050 to 1200 degrees Celsius for 30 to 60 minuteswith low oxygen (O2) and/or N2 is applied to diffuse the N+ draincontact region 220 and also to laterally diffuse the sidewall implantN-regions 225. The N-regions 225 now form a lateral N-type concentrationgradient, with the concentration being greatest near the deep trenchside walls. The sidewall implants may be used to adjust the N-typeconcentration of the regions of the substrate 205 that are along alateral direction relative to the deep trenches in order to achieve acharge balance (super-junction effect) with the P-epitaxial layer 230(about to be grown). Alternatively to the sidewall implants, thesubstrate 205 can be initially formed with the required N-typeconcentration to achieve the super junction effect. In FIG. 9E, theoxide layers 212 and 215 are etched off and a P-epitaxial layer 230 witha P dopant concentration of 1E15 to 1E16 or higher, is grown (dependingon the desired breakdown voltage). The thickness of the P-epitaxiallayer 230 is sufficient to fill the trenches 214. For a trench 214 witha width of about 3 microns, the thickness of the epitaxial layer 230over the top of the N-region 225 is approximately 1.5 to 2.0 microns. InFIG. 9F, an oxide layer is deposited with a thickness of about 0.5 to1.5 microns as hard-mask layer (not shown) followed by applying a gatetrench mask (not shown) to etch the hard-mask oxide layer then removingthe photoresist. The width of the gate trench may be of the order of 0.4to 1.5 micron typically. A silicon etch is carried out to etch thetrench gate openings 232 through the P-epitaxial layer 230 with a trenchdepth of about 1 to 2.5 microns that penetrates through the P-epitaxiallayer 230 into the N-dopant regions 225 between the epitaxial columns230 deposited into the trenches 212. The processes then followed withwafer cleaning and optionally a round hole etch to smooth the gatetrench profile followed by another wafer cleaning process.

In FIG. 9G, the oxide hard mask is removed followed by depositing a thinscreen layer 234 covering the sidewalls and the bottom surface of thegate trenches 232. Optionally, a trench sidewall-implant with a +/−7degrees tilt implant angle is carried out to compensate the P-epitaxiallayer 230 followed by a trench bottom implant with zero tilt angle tocompensate the P-epitaxial layer 230 if the gate trench 232 is tooshallow. The implants into the gate trench sidewalls and the bottomsurface to form the sidewall and bottom dopant regions 235-S and 235-Brespectively is to eliminate the sensitivity of the channel of theMOSFET device relative to the depth of the trench gates and the dopingconcentration of the P-epitaxial layer 230. In FIG. 9H, the screen oxidelayer 234 is removed and a thermal gate oxide layer 240 is grown havinga thickness of 0.01 to 0.1 micron depending on the device voltagerating. A gate polysilicon layer 245 is deposited into the gate trenches232. The gate polysilicon layer 245 is preferably performed with in-situN+ doping and the polysilicon layer 245 is doped by ion implantation ordiffusion, if the polysilicon layer 245 is not in-situ N+ doped. Thegate polysilicon layer 245 is etched back from the top surfacesurrounding the trenched gates 245.

In FIG. 9I, an optional body mask (not shown) is applied to carry out abody implant with boron for a NMOS device having a dosage ranging from3E12 to 1E14 followed by a body drive process at a temperature of 1000to 1150 degree Celsius to form the P-body regions 250 in the epitaxiallayer 230 surrounding the trench gates 245. In FIG. 9J, an optionalsource mask (not shown) is applied to carry out a source dopant implant.The source implant mask is optionally applied to protect the locationsto form the P-body contact. The source implant is carried out withsource dopant ions such as arsenic ions with a dosage about 4E15 at anenergy about 70 KeV at a zero degree tilt followed by a source annealoperation at a temperature of approximately 800 to 950 degrees Celsiusto diffuse the source regions 255. In FIG. 9K, a dielectric layer 260that by a Low Temperature Oxide deposition (LTO) and BPSG layer isformed to the top surface followed by a BPSG flow process. Then acontact mask (not shown) is applied to carry out an oxide etch to etchthe contact openings through the BPSG layer 260. A P+ body contactimplant is carried out as an optional step followed by a reflow afterthe body contact implant. In FIG. 9L, a barrier metal deposition iscarried out to cover the top surface with a barrier metal layer 265followed by a thick metal deposition to form the source metal layer 270.A metal mask (not shown) is applied to etch and pattern the source metaland gate connection metallization. The processes are completed with thedeposition of dielectric layers to passivate the device surface, and thepatterning of the passivation layer to form the bond, pad openings (notshown). A final alloy can then be performed. For the sake of brevity,these standard manufacturing processes are not specifically describedhere. In FIG. 9M, a backside grinding operation is carried out to removethe low doped portion of the substrate 205 from the bottom surface ofthe substrate then a back metal layer 210 is formed to contact the drainregion 220 where the dopant concentration is higher. The back metallayer 210 may be formed by a deposition of TiNiAg layer directly on thebackside of the wafers (below the drain region 220). The back grindingoperation has a thickness control with a few microns and even down toone micron thus enables a reliable backside contact to form the drainelectrode layer 210 to contact the N+ drain regions 220 near the bottomof the substrate 205.

Referring to FIGS. 10A to 10D for a series of cross sectional views forillustrating some of the processing steps in fabricating the MOSFETdevice with trench gates that have depth shallower the P-type epitaxiallayer 230. The processing steps as that shown in FIGS. 9A to 9F aresimilarly applied with the gate trenches 232 opened in the epitaxiallayer 230 surrounded by oxide hard mask layer 212. The gate trenches 232are shallower than the thickness of the epitaxial layer 230. The bottomsurface of the gate trenches 232 is above and at a distance from the Nsubstrate 225. The process is then followed with wafer cleaning andoptionally a round-hole etching process to smooth the gate trenchprofile followed by another wafer cleaning process. A thin layer ofscreen layer 234 is deposited on the sidewalls and the bottom surface ofthe gate trenches 232. In FIG. 10B, a trench sidewall sidewall-implantwith a +/−7 degrees tilt angle coordinated with rotational implant iscarried out optionally to compensate the P-epitaxial layer 230 followedby a trench bottom implant with zero tilt angle to compensate theP-epitaxial layer 230 due to the shallow gate trench 232. The implantsinto the gate trench sidewalls and the bottom surface to form thesidewall and bottom dopant regions 235-S and 235-B respectively is toeliminate the sensitivity of the channel of the MOSFET device relativeto the depth of the trench gates and the doping concentration of theP-epitaxial layer 230. The thick oxide hard mask 212 protects the topsurface from gate trench implant. In FIG. 10C, the screen oxide layer234 is removed and a thermal gate oxide layer 240 is grown having athickness of 0.01 to 0.1 micron depending on the device rating. A gatepolysilicon layer 245 is deposited or grown into the trenches 232. Thegate polysilicon layer 245 is preferably performed with in-situ N+polysilicon and the polysilicon layer 245 is doped by ion implantationif the polysilicon layer 245 is not in-situ N+ doped. The gatepolysilicon layer 245 is etched back from the top surface surroundingthe trenched gates 245. In FIG. 10D, an body mask (not shown) isoptionally applied to carry out a body implant with boron for a NMOSdevice having a dosage ranging from 3E12 to 1E14 followed by a bodydrive process at a temperature of 1000 to 1150 degree Celsius to formthe P-body regions 250 in the epitaxial layer 230 surrounding the trenchgates 245. The accumulation region and channel region are formedsurrounding and beneath the trench gate 245 even though the trench gate245 is shallower than the thickness of the P-epitaxial layer 230.Subsequent processing steps such as that shown in FIGS. 9J to 9M arecarried out to complete the fabrication processes of the MOSFET device.

FIG. 11 shows an alternate processing step that is different from theprocessing step shown in FIG. 9B. FIG. 11 shows the step of depositionof an oxide layer 215 or a thermal growth of a conformal oxide layer 215by applying a High Temperature deposited Oxide (HTO) process. Theprocesses then skip the step of a RIE anisotropic etch of the screenoxide in bottom of the deep trenches during the deep trench implantsteps. A drain contact implant is performed by implanting N+ ions alonga zero degree tilt angle relative to, the sidewalls of the trencheshaving an implant dosage greater than 1E15 and an implanting energyadjusted to penetrate the bottom oxide layer to form the drain contactregions 220 immediately below the deep trenches 214. The drain contactregion 220 may be implanted with N ions such as phosphorus or arsenicions. The oxide layer 215 along the sidewalls protects the sidewallsfrom the high dosage of the drain contact implant. Compared to thedevice shown in FIG. 9B, this embodiment has the advantages that it isnot required to carry out an etch-back step to remove the oxide at thebottom of the deep trenches, the manufacturing processes are simplifiedand the production cost is reduced.

Referring to FIGS. 12A to 12M for a serial of side cross sectional viewsto illustrate the processing steps for manufacturing a charge balancedsemiconductor power device as another exemplary embodiment of thisinvention. The purpose of the processing steps is to provide asimplified device from the above embodiments. As will be furtherdescribed below, the ion implantation at the bottom of the deeptrenches, as well as a high temperature anneal process to form a lowresistance drain contact diffusion at the bottom of the structure, isnot required since a highly doped substrate (with a grown N-epi on top)is used instead of a “bulk” wafer with uniform N doping. As discussedearlier, the term “top substrate layer” is used instead of “epitaxiallayer” for the starting silicon substrate, to avoid confusion.

FIG. 12A shows a starting silicon substrate comprises an N+ CZ bottomsubstrate 305 supports an N top substrate layer 310 grown on top of it.The N+ bottom substrate 305 is preferably a substrate with a resistivityin a range between 0.003 to 0.005 ohm/cm and the N top substrate layer310 for NMOS has a thickness that is dependent on the breakdown voltage.For a device having a breakdown voltage approximately 600 volts orhigher, a top substrate layer 310 having a thickness of 45 to 55 mm isused. A hard mask oxide layer 312 is deposited or thermally grown with athickness of 0.1 to 1.5 micrometer. Then a trench mask (not shown) witha critical dimension (CD) in a 1 to 5 microns range (preferable 3.0microns), is applied to carry out an oxide etch to open a plurality oftrench etching windows followed by removal of the photoresist. A siliconetch is carried out to open deep trenches 314 in the N top substratelayer 310 with a depth of 40 to 50 microns for devices operated at avoltage of about 650 volts. Depending on the type etcher and etchchemistries, photoresist only mask may also be used to pattern and openthe trench as well instead of using the hard mask oxide layer 312 asshown. The trench opening may be in the 1 micron to 5 microns rangepreferably 3 microns for most applications. Then a wafer cleanup processis performed. In this embodiment, the trenches do not reach the bottomsubstrate 305. In an alternative embodiment the trenches may be etcheddown to reach the bottom substrate 305. In FIG. 12B, a conformal oxidelayer 315 is formed by either an oxide deposition or thermal growthprocess. Then an optional RIE anisotropic etch is carried out to clearthe oxide from the bottom of the trench bottom surface if the oxidelayer is thicker on the bottom surface. The thickness of the oxide layer315 is between 0.015 to 0.1 microns when the process does not includethe optional RIE step and the layer thickness of the oxide layer 315 isbetween 0.1 to 0.4 micrometers when the processes include the optionalRIE step.

In FIG. 12C, a trench sidewall implant is carried out with N-type ionssuch as phosphorus ions to adjust the doping concentration in the N topsubstrate layer 310 An implant with tilted angle and rotated operationsare performed with a dosage of 5E11 to 2E13 and a tilt angle of five tofifteen degrees are carried out to form the N-regions 325 in the N topsubstrate layer 310 between the trenches depending on the trench depth.In FIG. 12D, a high temperature anneal operation at 1050 to 1200 degreesCelsius for 30 to 60 minutes with low oxygen (O2) and/or N2 is appliedto laterally diffuse the sidewall implant N-regions 325. Alternatively,the sidewall implants and anneal can be skipped, and the N top substratelayer 310 can be selected ahead of time to have the N-type concentrationrequired for the super-junction effect. In FIG. 12E, the oxide layers312 and 315 are etched off and a P-epitaxial layer 330 with a P dopantconcentration of 1E15 to 1E16 or higher, depending on the requiredbreakdown voltage, is grown. The thickness of the P-epitaxial layer 330is sufficient to fill the trenches 314. For a trench 314 with a width ofabout 3 microns, the thickness of the epitaxial layer 330 isapproximately 1.5 to 2.0 microns covering the top surface above thetrenches 314. In FIG. 12F, an oxide layer is deposited with a thicknessof about 0.5 to 1.5 microns as hard-mask layer (not shown) followed byapplying a gate trench mask (not shown) to etch the hard-mask oxidelayer then removing the photoresist. The width of the gate trench may beof the order of 0.4 to 1.5 microns typically. A silicon etch is carriedout to etch the trench gate openings 332 through the P-epitaxial layer330 with a trench depth of about 1 to 2.5 microns that penetratesthrough the P-epitaxial layer 330 into the N-dopant regions 325 betweenthe epitaxial columns 330 deposited into the trenches 312. The processis then followed with wafer cleaning and optionally a round hole etchingprocess to smooth the gate trench profile followed by another wafercleaning process.

In FIG. 12G, the oxide hard mask is removed followed by depositing athin screen layer 334 covering the sidewalls and the bottom surface ofthe gate trenches 332. A trench sidewall-implant with a +/−7 degreestilt implant angle is carried out optionally to compensate theP-epitaxial layer 330 followed by a trench bottom implant with zero tiltangle to compensate the P-epitaxial layer 330 if the gate trench 332 istoo shallow. The implants into the gate trench sidewalls and the bottomsurface to form the sidewall and bottom dopant regions 335-S and 335-Brespectively is to eliminate the sensitivity of the channel of theMOSFET device relative to the depth of the trench gates and the dopingconcentration of the P-epitaxial layer 330. In FIG. 12H, the screenoxide layer 334 is removed and a thermal gate oxide layer 340 is grownhaving a thickness of 0.01 to 0.1 micron: depending on the devicevoltage rating. A gate polysilicon layer 345 is deposited into thetrenches 332. The gate polysilicon layer 345 is preferably performedwith in-situ N+ doping and the polysilicon layer 345 is doped by ionimplantation or diffusion if the polysilicon layer 345 is not in-situ N+doped. The gate polysilicon layer 345 is etched back from the topsurface surrounding the trenched gates 345.

In FIG. 12I, an optionally body mask (not shown) is applied to carry outa body implant with boron for a NMOS device having a dosage ranging from3E12 to 1E14 followed by a body drive process at a temperature of 1000to 1150 degree Celsius to form the P-body regions 350 in the epitaxiallayer 330 surrounding the trench gates 345. In FIG. 12J, an optionalsource mask (not shown) is applied to carry out a source dopant implant.The source implant mask is optionally applied to protect the locationsto form the P-body contact. The source implant is carried out withsource dopant ions such as arsenic ions with a dosage about 4E15 at anenergy about 70 KeV at a zero degree tilt followed by a source annealoperation at a temperature of approximately 800 to 950 degrees Celsiusto diffuse the source regions 355. In FIG. 12K, a dielectric layer 360that by a low thermal oxidation (LTO) and BPSG layer is formed to thetop surface followed by a BPSG flow process. Then a contact mask (notshown) is applied to carry out an oxide etch to etch the contactopenings through the BPSG layer 360. A P+ body contact implant iscarried out as an optional step followed by a reflow after the bodycontact implant. In FIG. 12L, a barrier metal deposition is carried outto cover the top surface with a barrier metal layer 365 followed by athick metal deposition to form the source metal layer 370. A metal mask(not shown) is applied to etch and pattern the source metal and gatemetalization. The processes are completed with the deposition ofdielectric layers to passivate the device surface and the patterning ofthe passivation layer to form the bond pad openings (not shown). A finalalloy process can then be performed. For the sake of brevity, thesestandard manufacturing processes are not specifically described here. InFIG. 12M, an optional backside grinding operation is carried out toremove the a portion of the bottom of the N+ bottom substrate 305 then aback metal layer 320 is formed to contact the N+ bottom substrate 305 asthe drain electrode. The back metal layer 320 may be formed by adeposition of TiNiAg layer directly below the N+ bottom substrate 305.The back grinding operation has a thickness control with a few microns,and even down to one micron thus enables a reliable backside contact toform the drain electrode layer 320 to contact the N+ bottom substrate305.

Referring to FIGS. 13A to 13M for a serial of side cross sectional viewsto illustrate the processing steps for manufacturing a charge balancedsemiconductor power device as another exemplary embodiment of thisinvention. FIG. 13A shows a starting silicon substrate comprises an N+CZ bottom substrate 405 supports an N top substrate layer 410 grown ontop of it. The N+ bottom substrate 405 is preferably a substrate with aresistivity in a range between 0.003 to 0.005 ohm/cm and the N topsubstrate layer 410 for NMOS has a thickness that is dependent on thebreakdown voltage. For a device having a breakdown voltage approximately600 volts or higher, a top substrate layer 410 has a thickness of 45 to55 microns is used. A hard mask oxide layer 412 is deposited orthermally grown with a thickness of 0.1 to 1.5 micrometer. Then a trenchmask (not shown), with a critical dimension (CD) in a 1 to 5 micronsrange (preferable 3.0 microns), is applied to carry out an oxide etch toopen a plurality of trench etching windows followed by removal of thephotoresist. A silicon etch is carried out to open deep trenches 414 inthe top substrate layer 410 with a depth of 40 to 50 microns for devicesoperated at a voltage of about 650 volts. Depending on the type etcherand etch chemistries, photoresist only mask may also be used to patternand open the trench as well instead of using the hard mask oxide layer412 as shown. The trench opening may be in the 1 micron to 5 micronsrange preferably 3 microns for most applications. Then a wafer cleanupprocess is performed. In FIG. 13B, a conformal oxide layer 415 is formedby either an oxide deposition or thermal growth process. Then anoptional RIE anisotropic etch is carried out to clear the oxide from thebottom of the trench bottom surface if the oxide layer is thicker on thebottom surface. The thickness of the oxide layer 415 is between 0.015 to0.1 mm when the process does not include the optional RIE step and thelayer thickness of the oxide layer 415 is between 0.1 to 0.4 micrometerswhen the processes include the optional RIE step.

In FIG. 13C, a trench sidewall implant is carried out with N-type ionssuch as phosphorous ions to set the doping concentration in the Nregions. An implant with tilted angle and rotated operations areperformed with a dosage of 5E11 to 2E13 and a tilt angle of five tofifteen degrees and rotational implants are carried out to form theN-regions 425 between the trenches depending on: the trench depth. InFIG. 13D, a high temperature anneal operation at 1050 to 1200 degreesCelsius for 30 to 60 minutes with low oxygen (O2) and/or N2 is appliedto laterally diffuse the sidewall implant N-regions 425 through the topsubstrate layer 410. In FIG. 13E, the oxide layers 412 and 415 areetched off and a P-epitaxial layer 430 with a P dopant concentration on1E15 to 1E16 is grown. The thickness of the P-epitaxial layer 430 issufficient to fill the trenches 414. For a trench opening 414 with adepth of about 3 microns, the thickness of the epitaxial layer 430 isapproximately 1.5 to 2.0 microns having a thickness higher than half ofthe trench critical dimension (CD) covering the top surface above thetrenches 414. In FIG. 13F, a partial etch back of the P-epitaxial layer430 is carried out by applying a chemical mechanical planarization (CMP)or a RIE process leaving a planar layer of the P-epitaxial layer 430 onthe top surface. In FIG. 13G, an oxide layer is deposited with athickness of about 0.5 to 1.5 microns as hard-mask layer (not shown)followed by applying a gate trench mask (not shown) to etch thehard-mask oxide layer then removing the photoresist. A silicon etch iscarried out to etch the trench gate openings 432 through the P-epitaxiallayer 430 with a trench depth of about 1 to 2.5 microns that penetratesthrough the P-epitaxial layer 430 into the N-dopant regions 425 betweenthe epitaxial columns 430 deposited into the trenches 412. The processesthen followed with wafer cleaning and optionally a round hole etch tosmooth the gate trench profile followed by another wafer cleaningprocess.

In FIG. 13H, the oxide hard mask is removed followed by depositing athin screen layer 434 covering the sidewalls and the bottom surface ofthe gate trenches 432. A trench sidewall-implant with a +/−7 degreestilt implant angle is carried out optionally to compensate theP-epitaxial layer 430 followed by a trench bottom implant with zero tiltangle to compensate the P-epitaxial layer 430 if the gate trench 432 istoo shallow. The implants into the gate trench sidewalls and the bottomsurface to form the sidewall and bottom dopant regions 435-S and 435-Brespectively is to eliminate the sensitivity of the channel of theMOSFET device relative to the depth of the trench gates and the dopingconcentration of the P-epitaxial layer 430. In FIG. 13I, the screenoxide layer 434 is removed and a thermal gate oxide layer 440 is grownhaving a thickness of 0.01 to 0.1 micron depending on the device rating.A gate polysilicon layer 445 is deposited into the trenches 432. Thegate polysilicon layer 445 is preferably performed with in-situ N+polysilicon and the polysilicon layer 445 is doped if the polysiliconlayer 445 is not in-situ N+ polysilicon. The gate polysilicon layer 445is etched back from the top surface surrounding the trenched gates 445.

In FIG. 13J, an optional body mask (not shown) is applied to carry out abody implant with boron for a NMOS device having a dosage ranging from3E12 to 1E14 followed by a body drive process at a temperature of 1000to 1150 degree Celsius to form the P-body regions 450 in the epitaxiallayer 430 surrounding the trench gates 445. In FIG. 13K, an optionalsource mask (not shown) is applied to carry out a source dopant implant.The source implant mask is optionally applied to protect the locationsto form the P-body contact. The source implant is carried out withsource dopant ions such as arsenic ions with a dosage about 4E15 at anenergy about 70 Kev at a zero tilt degree followed by a source annealoperation at a temperature of approximately 800 to 950 degrees Celsiusto diffuse the source regions 455. In FIG. 13L, a dielectric layer 460that by a local thermal oxidation (LTO) and BPSG layer is formed to thetop surface followed by a BPSG flow process. Then a contact mask (notshown) is applied to carry out an oxide etch to etch the contactopenings through the BPSG layer 460. A P+ body contact implant iscarried out as an optional step followed by a reflow after the bodycontact implant. In FIG. 13M, a barrier metal deposition is carried outto covering the top surface with a barrier metal layer 465 followed by athick metal deposition to form the source metal layer 470. A sourcemetal mask (not shown) is applied to etch and pattern the source metalcontact layer to contact the source/body regions. The processes arecompleted with the formation and the patterning of the passivation layerand the formation and the patterning of the contact pads with a finalalloy process. Furthermore, a backside grinding operation is carried outto remove the bottom portion of the N+ bottom substrate 405 from thebottom surface of the substrate then a back metal layer (notspecifically shown) is formed to contact the bottom substrate 405 as thedrain electrode. The back metal layer may be formed by a deposition ofTiNiAg layer directly below the bottom substrate 405. The back grindingoperation has a thickness control with a few microns and even down toone micron thus enables a reliable backside contact to form the drainelectrode layer to contact the N+ bottom substrate 405 near the bottomof the substrate. For the sake of brevity, these standard manufacturingprocesses are not specifically described here or shown in the figures.The processing steps are similar to that shown in FIGS. 9A to 9L butwith a partial CMP of the P-epitaxial layer to smooth out theP-epitaxial layer 430. This alternate embodiment has the advantage ofhaving a smooth out P-epi surface. It also enables the use of shallowergate trench. The partial CMP of the P-epitaxial layer may also beapplied to other embodiments of the invention.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is not to be interpreted as limiting. For example, though theabove describes an n-channel device, this invention can be applied top-channel devices as well simply by reversing the conductivity types ofthe doped regions. Various alterations and modifications will no doubtbecome apparent to those skilled in the art after reading the abovedisclosure. Accordingly, it is intended that the appended claims beinterpreted as covering all alterations and modifications as fall withinthe true spirit and scope of the invention.

I claim:
 1. A semiconductor power device comprising: a semiconductorsubstrate comprising a bottom substrate and a top substrate layer grownover the bottom substrate, wherein the top substrate layer and thebottom substrate are of a same conductivity type, wherein thesemiconductor substrate further includes it plurality of deep trenches;an epitaxial layer filling said deep trenches, the epitaxial layerfurther including a simultaneously grown top epitaxial layer coveringareas above a top surface of said deep trenches and over saidsemiconductor substrate, wherein the epitaxial layer is of an oppositeconductivity type as the semiconductor substrate; a plurality of trenchMOSFET cells disposed in said to epitaxial layer with the top epitaxiallayer acting as the boil region and the semiconductor substrate actingas the drain region whereby a super-junction effect is achieved throughcharge balance between the portions of the epitaxial layer in the deeptrenches and the portions of the top substrate layer lateral to the deeptrenches; and each of said plurality of trench MOSFET cells includes atrench. DMOS transistor cell having a trench gate opened through saidtop epitaxial layer having a gate trench depth less than or equal to athickness of said top epitaxial layer and said trench gate is filledwith it gate dielectric material and a gate conductor material, the gatetrench further comprising gate sidewall dopant regions surroundingsidewalk of said trench gate and a gate-bottom dopant region below saidtrench gate, wherein the gate sidewall dopant regions and gate-bottomdopant regions are of a same conductivity type as the semiconductorsubstrate.
 2. A semiconductor power device comprising: a semiconductorsubstrate comprising a bottom substrate and a top substrate layer grownover the bottom substrate, wherein the top substrate layer and thebottom substrate are of a same conductivity type, wherein thesemiconductor substrate further includes a plurality of deep trenches;epitaxial layer filling said deep trenches, the epitaxial layer furtherincluding a simultaneously grown top epitaxial layer covering areasabove, a top surface of said deep trenches and over said semiconductorsubstrate, wherein the epitaxial layer is of an opposite conductivitytype as the semiconductor substrate; a plurality of trench MOSFET cellsdisposed in said top epitaxial layer with the top epitaxial layer actingas the body region and the semiconductor substrate acting as the drainregion whereby a super-junction effect is achieved through chargebalance between the portions of the epitaxial layer in the deep trenchesand the portions of the top substrate layer lateral to the deeptrenches; and said semiconductor substrate further includes a lateraldoping concentration gradient with the concentration being the highestnext to the deep trench sidewalls.
 3. The semiconductor power device ofclaim 2 wherein: each of said plurality of trench MOSFET cells includesa trench DMOS transistor cell having a trench gate opened through saidtop epitaxial layer and penetrating into a top portion of saidsemiconductor substrate and said trench gate is filled with a gatedielectric material.
 4. The semiconductor power device of claim 2wherein: the bottom of the deep trenches reaches the bottom substrate.5. The semiconductor power device of claim 2 wherein: the bottom of thedeep trenches does not reach the bottom substrate.
 6. A semiconductorpower device comprising: a semiconductor substrate comprising a bottomsubstrate and a top substrate layer grown, over the bottom substrate,wherein the top substrate layer and the bottom substrate are of a sameconductivity type, wherein the semiconductor substrate further includesa plurality of deep trenches; an epitaxial layer filling said deeptrenches, the epitaxial layer further including a simultaneously growntop epitaxial layer covering areas above a top surface of said deeptrenches and over said semiconductor substrate, wherein the epitaxiallayer is of an opposite conductivity type as the semiconductorsubstrate; a plurality of trench MOSFET cells disposed in said topepitaxial layer with the top epitaxial layer acting as the body regionand the semiconductor substrate acting as the drain region whereby asuper-junction effect is achieved through charge balance between theportions of the epitaxial layer in the deep trenches and the portions ofthe top substrate layer lateral to the deep trenches; each of said DMOStransistor cells further having gate sidewall do ant regions surroundingsidewalk of said trench gate and a gate-bottom dopant region below saidtrench gate, wherein the gate sidewall dopant regions and gate-bottomdopant regions are of a same conductivity type as the semiconductorsubstrate.
 7. The semiconductor power &vice of claim 6 wherein: each ofplurality of trench MOSFET cells includes a trench DMOS transistor cellhaving a trench gate opened through said top epitaxial layer andpenetrating into a top portion of said semiconductor substrate and saidtrench gate is filled with a gate dielectric material.
 8. Thesemiconductor power device of claim 6 wherein the bottom of the deeptrenches reaches the bottom substrate.
 9. The semiconductor power deviceof claim 6 wherein: the bottom of the deep trenches does no roach thebottom substrate.